185/.] SALTER DEVONIAN PLANT-REMAINS. 77 



of the boundary-line between Sutherland and Caithness, the gneissose 

 rocks of the Highlands extend into Caithness to the distance of 

 from three to eight miles, and are succeeded by the Old Red Sand- 

 stone, which stretches in one unbroken deposit eastward to the 

 German Ocean and northward to the Northern Ocean. Along the 

 whole of the line of junction of the two deposits, the rocks are so 

 covered with moss and heath that it is extremely difficult to get at 

 the base of the Old Red Sandstone ; at the Ord of Caithness, how- 

 ever, in the sea-cliffs immediately under the celebrated mountain- 

 pass of that name, very fine sections may be seen of the great fos- 

 siliferous conglomeratic base of the Devonian or Old Red. From 

 the Ord of Caithness northwards to Duncansbay Head, and from 

 Duncansbay Head westwards to Sandside Head, the seaboard of 

 the county is composed of a range of mural precipices, from 40 to 

 nearly 400 feet in height ; and the whole of the Devonian portion of 

 the county northwards of the Morven and Scarabin Hills is an 

 elevated plateau, rising abruptly out of the sea, but seldom attaining 

 a greater height than 500 feet above the sea-level in any part of the 

 interior. The strata are inclined at low angles, generally dipping 

 towards the north-west, and sometimes almost horizontal; and 

 throughout the greater portion, wherever a quarry has been opened, 

 at the foot of the cliffs, on the sea-shore, or on the tops of the hills, 

 the practised eye can detect fragments of plants mixed with the 

 bones and scales of fish. The most entire and largest specimens, 

 however, of plants have been hitherto found in the neighbourhood 

 of Thurso, in the flagstone-quarries, which are numerous in that 

 locality. 



DESCRIPTION OF PLATE V., 



Illustrative of Fossil Plants from Caithness and Orkney. 



Fig. la. Fragment of a large, straight, compressed, finely fluted, bituminized, stem- 

 like body ; from a quarry three miles west of Thurso. One-fourth of the 



natural size. (Mr. J. Miller's collection.) 

 Fig. lb. Portion of the finely fluted surface ; magnified. 

 Fig. \c. Traces of woody structure, showing the remains of pitted fibre, with a 



double row of pits or disks. Highly magnified. 

 Fig. 2. Fragment of a large, curved, compressed, bituminized root-like (?) body; 



from a quarry four miles east of Thurso. One-fourth natural size. 



(Mr. J. Miller"'s collection.) 

 Fig. 3. Dichotomous rootlet ; from Kilminster, Wick. Natural size. (Geological 



Survey collection.) 

 Fig. 4. Dichotomous root ; from Kilminster, Wick. Natural size. (Geological 



Survey collection.) The oval mark in the specimen is the outline of an 



Annelide-burrow. 

 Fig. 5. Branched root, marked with fine tubercles, which have somewhat of a 



spiral arrangement. Natural size. From Dale Quarry, Stromness. 



(Geological Survey collection.) 

 Fig. 6. Branched rootlet lying on a flagstone which presents traces of Annelide- 



burrows {Arenicolites), frequently in pairs. Kilminster, Wick. Natural 



size. (Geological Survey collection.) 

 Fig. 7a. Terminal rootlet with lateral tubercles. 

 Fig. 7b. The terminal tubercles, magnified. 



